Conventionally, tractors used for a farm field have been known (for example Patent Literature 1). The tractor has a front portion provided with a bonnet, and an engine installed in the bonnet. The bonnet includes an upper cover and a pair of lower covers.
The bonnet is required to enable air to flow into and out of the bonnet. This is for supplying outer air to the engine and for preventing heat produced by engine from accumulating in the bonnet. When an opening part is provided to the bonnet, the rigidity of the bonnet might be compromised due to the shape or the like of the opening part. Thus, a bonnet achieving a higher flowability of air while maintaining a high rigidity has been called for.